The multi-axle drive train can be used for a motor vehicle, for example, and can be a component of the motor vehicle, in particular. The multi-axle drive train makes it possible to drive a plurality of axles—for example, the first axle, in particular a front axle, and the second axle, in particular a rear axle—of the motor vehicle. An operative connection between the axles of the motor vehicle can be produced in this case via a connecting shaft, which, for example, is present as a Cardan shaft. Often, it is desirable that a multi-axle operation is carried out by means of the multi-axle drive train only intermittently, during which time a plurality of the axles are actually driven. In the case of a motor vehicle, this is necessary, for example, only if the traction would be too small when only one of the axles is driven and/or if the desired driving performance can be realized only with a multi-axle drive. Therefore, it is often appropriate to drive only one of the axles, namely the first axle, by means of the multi-axle drive train.
For this reason, the first axle is operatively connected permanently to the drive device. In this case, the drive device has, for example, at least one drive assembly, in particular an internal combustion engine. Furthermore, the drive device can comprise at least one transmission gearbox and/or one starting clutch. The second axle is operatively connected via the clutch to the drive device. When the clutch is open, the operative connection between the drive device and the second axle is insofar disengaged. When the clutch is at least partly, in particular fully closed, in contrast, at least a portion of the torque supplied by the drive device is transmitted to the second axle. An embodiment of this kind for the multi-axle drive train may be referred to, for example, as a “hang on” drive train.
If the clutch is closed, then both the first axle and the second axle are driven by means of the drive device, and thus the torque supplied by the drive device is distributed between them based on the potential power that can be delivered to each axle. If the engageable second axle cannot transmit adequate torque because, for example, the coefficient of friction between the wheels of the second axle and an underlying ground of the motor vehicle is too small, in particular because the wheels are resting on ice, the torque of the drive device that cannot be transmitted via the second axle is delivered to the rigidly coupled first axle.
The first consequence thereof is that the first axle or the operative connection between the drive device and the first axle has to be designed in such a way that the entire torque that can be supplied by the drive device shall be applied to the first axle without the expectation of any damage. Alternatively, it is provided that the maximum torque of the drive device is reduced by the specific safety value when the second axle is coupled to the drive device.
In this case, the specific safety value corresponds preferably to the difference between the maximum torque of the drive device and the maximum torque that is to be transmitted to the first axle and for which no damage is expected to occur. The maximum torque, minus the specific safety value, thus corresponds to this torque, which can be delivered without any problem to the first axle or can be transmitted via the first axle. The maximum torque is understood to mean the torque that is maximally produced by the drive device or shall be maximally delivered to the first axle and/or to the second axle. The torque supplied by the drive device is insofar limited upward, that is, in the direction of larger values, to the maximum torque. The torque supplied by the drive device or delivered to the first axle and/or to the second axle should therefore always be less than or equal to the maximum torque.